Abstract
The control of the droplet shape during the impact on a solid surface is of relevance for several practical applications, such as inkjet printing technologies. Although several studies have reported factors affecting the final droplet shape, understanding of the liquid spreading process is still lacking. In this work, droplets of different velocities are deposited on surfaces patterned with conical and cylindrical pillars. It is shown that for the structures of the same height and pitch, the shape of the lateral wall of the micro-structures affects the droplet shape. In addition, at higher deposition velocity, the initial polygonal/square shape of the droplets evolves into a more circular shape. The change in the shape due to the lateral wall of the structures is the result of the solid–liquid contact both above and below the structures and the way in which the liquid is able to move in between the structures for different passage areas.
Highlights
INTRODUCTIONStructured surfaces have been the focus of research during the last few years as a way to manipulate wetting properties in applications where droplet manipulation is important, such as inkjet printing, liquid metal printing, and solder droplet printing
55 ± 5 63 ± 3 74 ± 4 capillary force on the observed phenomena) while keeping the surface tension in the range where Wenzel-state droplets were obtained on the tested surfaces for the purposes of this study
Experiments were performed with three different mixtures of DI water and ethanol in order to vary the liquid surface tension, resulting in Wenzel state droplets for the tested surfaces
Summary
Structured surfaces have been the focus of research during the last few years as a way to manipulate wetting properties in applications where droplet manipulation is important, such as inkjet printing, liquid metal printing, and solder droplet printing.. Faceted droplets during the impact on superhydrophobic pillar arrangements have been explained by the partial penetration of the liquid into the structures for larger We numbers and by the capillary and viscous forces retarding the movement of the contact line in different directions between adjacent pillars.. Faceted droplets during the impact on superhydrophobic pillar arrangements have been explained by the partial penetration of the liquid into the structures for larger We numbers and by the capillary and viscous forces retarding the movement of the contact line in different directions between adjacent pillars.24,27 All these droplet impact studies have been performed on superhydrophobic surfaces with microstructures with vertical lateral walls, where both Cassie and Wenzel wetting states were observed. In addition to the shape of the lateral wall of structures, both the pitch distance of the microstructures and impacting velocity can be used to control the final droplet shape
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